Magnetic material, magnetic impulse recording members, and methods of making magnetic material



United States Patent 3,115,470 MAGNETIC MATERIAL, MAGNETIC IMPULSE RECORDING MEMBERS, AND METHOD OF MAKING MAGNETIC MATERIAL Robert F. Conley, Elizabeth, Ni, assignor to Georgia Kaolin Company, Elizabeth, N.J., a corporation of New Jersey No Drawing. Filed Mar. 29, 1951, Ser. No. 99,036

1 i Claims. (Cl. 252-625) This invention relates to magnetic materials and methods of making magnetic material and to magnetic impulse recording members. More specifically this invention relates to the preparation of ferromagnetic material for use in a magnetic impulse record member such as a tape, ribbon, sheet or the like, coated or impregnated with a ferromagnetic surface layer of magnetic material.

The manufacture of magnetic sound recorder tapes is not new. Non-magnetic backing sheets such as tapes, ribbons or sheets or the like of paper, plastic etc. have been provided with a magnetic oxide coating for the purpose of sound recording. The magnetic materials heretofore available have been subject to a variety of deficiencies and many attempts have been made to produce a material which would be completely satisfactory. The general history of this problem is described in Camras Patent 2,694,656 and a solution is there proposed. However, even with all of these efforts to produce satisfactory materials, all previous magnetic materials have suffered from an inability of the industry to produce magnetic materials of a sulliciently small size for maximum frequency range and noise elimination. This problem is one of many facets. The filtration and Washing of very small particles is extremely difficult. As a result particles smaller than about 0.5 micron are difiicult to attain. Aging to produce these large particles which can be filtered can result in loss of magnetism through reversion of the magnetic forms gamma Fe O and Fe O to the nonmagnetic alpha form. Drying also poses problems, because elevated temperatures cause crystal growth while, as pointed out above, aging does the same. It therefore becomes a choice of one of two evils. The net result is that the industry has been limited in the size, shape and magnetic properties of the oxide which it could produce.

I have discovered a magnetic material and method of producing it which eliminates these ditficulties. I have found that a magnetic iron oxide material can be produced in which the mean particle size may be considerably below 0.1 micron.

The material of my invention will have a coercivity between 200 to 300 oersteds, remanence above 1000 gauss, saturation induction above 2000 gauss and a ratio of saturation induction to remanence (Em/Br) less than 3. Such characteristics are essential to any faithful reproduction of a signal and to the production of a stable magnetic image.

The material and practice of my invention will perhaps be best understood by reference to the following example.

A finely divided kaolin having a mean particle size of 0.15 micron in average spherical diameter was formed into an aqueous slurry at 80 C. with FeSO -7H O in the proportion of about 80 parts of kaolin to 70 parts of FeSO -7H O. Concentrated NaOH was slowly added to a pH of about 10. The precipitate was agitated for about 10 minutes, filtered and washed and oven dried for 16 hours at 70 C., 6.25 grams of the dried precipitate were then added to 1250 cc. of water at 80 C. into which were added 352.5 grams FeSO -7H O, 1.25 grams NH OH-HCI. Concentrated NaOl-l was slowly added to a pH of 10. The precipitate was agitated for 10 minutes, filtered, Washed to remove salts and oven dried for 16 hours at 70 C. Forty grams of the dried product, a

3,115,470 Patented Dec. 24, 1963 very active and unstable hydrated delta Fe O were then heated in 100 grams of high viscosity (350-500 Saybolt seconds at 100 F.) mineral oil for 2 hours at 350 C. The material was then extracted twice with 500 cc. methyl chloroform, refluxed for 3 hours and oven dried at 100 C. for 16 hours.

The final dried material had a coercivity (Hc) of 213 oersteds, a saturation reduction (Bm) of 4450 gauss a remanence (Br) of 1910 gauss and a Bm/Br value of 2.33. Computations based on surface area indicate a mean particle size of the particles at 0.062 micron. These sizes were confirmed by electromicrographs. Analysis shows the iron to be the form of acicular ferric oxide. The iron oxide is a dark brown color, very stable and has magnetic properties similar to magnetite. X-ray crystallographic studies indicate the iron oxide to be at some stage between 5Fe O and Fe O While I prefer to precipitate the iron oxide onto the kaolin particles in a two stage process as described above similar results can be achieved by precipitating the iron oxide as a single step, drying, heating in oil and extracting as described above. In either case the filtration step is easily accomplished.

I have found that the precipitation should be carried out at temperatures below about 100 C. and at or above about C. for best results and at a terminal pH of about 10. Precipitation carried out below about 80 C. Will give satisfactory results if the product is heated for a longer period of time in the mineral oil. The pH value may vary between 9 and 11 but preferably should be held within :3 of pH 10, both from the standpoint of product quality and economical use of NaOH.

Drying of the precipitate prior to heating in oil should be in the temperature range of 7075 C. Higher temperatures induce growth of iron oxide particle size and decompose the very active delta phase. Lower temperatures require longer drying which likewise induces particle size growth.

The step of heating in oil should be carried out above 325 C. and preferably above 350 C. The upper limit of the oil heating step appears to be limited only by the flash point of the oil. The length of time does not appear to be critical in this step, however, excessive times are uneconomical not only because of the time loss but because of oil loss due to evaporation and decomposition. Mineral oils appear to have the peculiar ability to react in some Way, evidently resulting in a chain cracking because acrid vapors, most likely aldehyde and unsaturated derivatives of cracked chains, are given off and the final viscosity is perceptibly lower and the color darker. Mineral oil that has been used once appears to be more reactive in the process and should continue to be used when possible.

Other strongly acidic silanol group carrier agents may be substituted for kaolin. For example I have carried out the process outline in the example above using sodium bentonite having a mean particle size of about 0.1 micron instead of kaolinite with substantially identical results. Other mineral silicates and highly hydroxyl ated silica carry strongly acidic silanol groups and may likewise be used as the carrier with like results.

In the example described above the NH OH-HCI is employed to reduce decomposition of the delta phase to the alpha phase during precipitation. Although its use is preferred, it is not essential and may be omitted.

While I prefer to use methyl chloroform for solvent stripping by refluxing, I have found that any organic solvent for mineral oil may be used. For example I have used toluene with complete success.

In addition to bringing about stabilization of magnetic properties, the oil heating process results in the formation of unexpected and very useful surface chemical 6. A magnetic impulse record member having a nonmagnetic carrier and a coating iadherently bonded thereto of a binder and magnetic material, said magnetic material consisting essentially of finely divided kaolinite particles having absorbed thereon magnetic ferric oxide particles formed by precipitating iron oxide onto the kaolinite particles and converting to oxide in heated mineral oil.

7. The method of making ermanent magnet material which comprises precipitating iron oxid from fluid suspension on-to kaolinite particles, having a mean particle size less than about 0.5 micron removing the suspending fluid, heating the residue in mineral oil to effect re- Table I T. H A ed T. T. 110, Bm, Br, Sample pt., p pt. fir. dry, oil, Oil 0e. auss gauss Bm/Br While I have illustrated and described certain preferred practices and embodiments of my invention in the foregoing description, it will be understood that this in vention may be otherwise embodied within the scope of the following claims.

I claim:

1. The method of making permanent magnet material which comprises precipitating iron oxide from fluid suspension onto finely divided kaolinite particles, removing the suspending fluid, heating the residue in mineral oil to effect reduction of the iron to ferric oxide and extracting said mineral oil.

2. The method of making permanent magnet material which comprises precipitating iron oxide as ferric hydroxide onto finely divided kaolinite particles in aqueous suspension, removing the aqueous suspending medium, heating the resulting residue in mineral oil to effect conversion of the ferric hydroxide to ferric oxide and extracting said mineral oil from the ferric oxide.

3. The method of making permanent magnet material which comprises precipitating iron oxide as ferric hydroxide onto finely divided kaolinite particles in aqueous suspension in proportions of about 80% kaolinite and 20% ferric hydroxide, removing the aqueous suspending fluid, resuspending the resulting residue in aqueous suspension, precipitating an additional amount of ferric hydroxide onto the particles of suspended residue in an amount sufficient to make a total of between about 90% to about 98% by Weight of the total solids removing the aqueous suspending medium, heating the resulting residue in mineral oil to effect conversion of the ferric hydroxide to ferric oxide and extracting said mineral oil from the ferric oxide.

. 4. A permanent magnet material consisting essentially of finely divided kaolinite particle, having adsorbed thereon magnetic ferric oxide particles formed by precipitating iron oxide onto the kaolinite particles and converting to oxide in heated mineral oil.

5. A permanent magnet material consisting essentially of about 2% to 10% finely divided kaolinite particles having adsorbed thereon about 90% to 98% of ferric oxide particles formed by precipitating iron oxide ontothe kaolinite particles and converting to oxide in heated mineral oil,

duetion of the iron to ferric oxide and extracting said mineral oil.

8. The method of making permanent magnet material which comprises precipitating iron oxide as ferric hydroxide onto kaolini-te particles having a mean particle size less than about 0.5 micron in aqueous suspension, at a pH between about 9 and 11, removing the aqueous suspending medium, heating the resulting residue in mineral oil to a temperature above about 325 C. to effect conversion of the ferric hydroxide to ferric oxide and extracting said mineral oil from the ferric oxide wit-h an organic solvent for said mineral oil.

9. The method of making permanent magnet material which comprises precipitating iron oxide as ferric hydroxide onto finely divided kao-linite particles in aqueous suspension in proportions of about kaolinite and 20% ferric hydroxide, at a terminal pH between about 9 to ll removing the aqueous suspending fluid, resuspending the resulting residue in aqueous suspension, preci itating an additional amount of ferric hydroxide onto the particles of suspended residue at a terminal pH between about 9 to 11 in an amount sufiicient to make a total of between about to about 98% ferric oxide by weight on the total solids, removing the aqueous suspending medium, heating the resulting residue in mineral oil to a temperature above about 325 C. to eifect conversion of the ferric hydroxide to ferric oxide and extracting said mineral oil from the ferric oxide with an organic solvent for said mineral oil.

10. A permanent magnet material consisting essentially of finely divided kaolinite particle, having adsorbed thereon magnetic ferric oxide par-ticles formed by precipitating iron hydroxide onto the kaolinite particles and converting to oxide in heated mineral oil at a temperature above about 325 C.

11. A permanent magnet material consisting essentially of about 2% to 10% finely divided kaolinite particles having adsorbed there-on about 90% to 98% of ferric oxide particles formed by precipitating iron hydroxide onto the kaolinite particles and converting to oxide in heated mineral oil at a temperature above about 325 C.

12. A magnet impulse record member having a nonmagnetic carrier and a coating adherently bonded thereto of a binder and magnetic material, said magnetic material consisting essentially of finely divided kaolinitc particles having adsorbed thereon magnetic ferric oxide particles formed by precipitating iron hydroxide onto the kaolinite particles and converting to oxide in heated mineral oil at a temperature above about 325 C.

13. The method of making permanent magiet mate rial which comprises precipitating iron as ferric hydroxide onto finely divided kaolinite particles in aqueous suspension in proportions of about 80% kaolinite and 20% ferric hydroxide, at a terminal pH of about filtering the solids from said suspension, resuspending the resulting solids in aqueous suspension, precipitating an additional amount of ferric hydroxide onto the particles of suspended solids in an amount suificient to make a total of between about 90% to about 98% by Weight of ferric oxide on the total solids at a terminal pH of about 10, filtering the resulting solids, heating the resulting solids in mineral oil at a temperature of 350 C. to effect conversion oft he ferric hydroxide to ferric oxide and extracting said mineral oil from the ferric oxide by refluxing in methyl chloroform.

14. A permanent magnet material consisting essentially of about 2 to 10% finely divided kaolinite particle having a mean particle size less than about 0.5 micron having adsorbed thereon about 90% to 98% of magnetic ferric oxide particles formed by precipitating ferric hydroxide onto the kaolinite particles and converting said ferric hydroxide to oxide in heated mineral oil at a temperature above about 350 C.

15. The method of making permanent magnet material which comprises precipitating iron hydroxide from fluid suspension onto finely divided particles carrying highly acidic silanol groups, removing the suspending fluid, heating the residue in mineral oil to effect reduction of the iron to ferric oxide and extracting said mineral oil.

16. The method of making permanent magnet material which comprises precipitating iron as ferric hydroxide onto finely divided particles carrying highly acidic silanol groups in aqueous suspension, removing the aqueous suspending medium, heating the resulting residue in mineral oil to effect conversion of the ferric hydroxide to ferric oxide extracting said mineral oil from the ferric oxide.

17. The method of making permanent magnet material which comprises precipitating iron as ferric hydroxide onto finely divided particles carrying highly acidic silanol groups in aqueous suspension in proportions of about of said silanol carryin particles and 20% ferric hydroxide, removing the aqueous suspending fluid, resuspending the resulting residue in. aqueous suspension, precipitating an additional amount of ferric hydroxide onto the particles of suspended residue in an amount sufiicient to make a total of between about to about 98% by weight on the total solids removing the aqueous suspending medium, heating the resulting residue in mineral oil to effect conversion of the ferric hydroxide to ferric oxide and extracting said mineral oil from the ferric oxide.

18. A permanent magnet material consisting essentially of finely divided particles carrying highly acidic silanol groups having adsorbed thereon magnetic ferric oxide particles formed by precipitating iron hydroxide onto the particles carrying silanol groups and converting to oxide in heated mineral oil.

19. A permanent magnet material consisting essentially of about 2% to 10% finely divided particles carrying highly acidic silanol groups having adsorbed thereon about 90% to 98% of ferric oxide particles formed by precipitating iron hydroxide onto the silanol groups of said particles and converting to oxide in heated mineral oil.

2 0. A ma net impulse record member having a nonmagnetic carrier and a coating adherently bonded thereto of a binder and magnetic material, said etic material consisting essentially of finely divided particles carrying highly acidic silanol groups having adsorbed thereon magnetic ferric oxide particles formed by precipitating iron hydroxide onto the silanol groups of said particles and converting to oxide in heated mineral oil.

References fitted in the file of this patent UNITED STATES PATENTS 2,582,590 Heeren et al Ian. 15, 1952 2,657,149 llcr Oct. 27, 1953 2,694,656 Camras Nov. 16, 1954 3,007,807 Radocy -2 Nov. 7, 1961 FOREIGN PATENTS 450,776 Canada Aug. 24, 1948 799,912 Great Britain Aug. 13, 1958 

1.THE METHOD OF MAKIN PERMANENT MAGNET MATERIAL WHICH COMPRISES PRECIPITATING IRON OXIDE FROM FLUID SUSPENSION ONTO FINELY DIVIDED KAOLINITE PARTICLES, REMOVING THE SUSPENDING FLUID, HEATING THE RESIDUE IN MINERAL OIL TO EFFECT REDUCTION OF THE IRON TO FERRIC OXIDE AND EXTRACTING SAID MINERAL OIL. 